The invention relates to electrostatic precipitators or collectors, including for use in internal combustion engine electrostatic crankcase ventilation systems, including for diesel engines.
Electrostatic precipitators or collectors, also known as electrostatic droplet collectors, are known in the prior art. In its simplest form, a high voltage corona discharge electrode is placed in proximity to a collector electrode, for example a high voltage corona discharge electrode is placed in the center of a grounded canister or tube forming an annular ground plane providing a collector electrode around the discharge electrode. A high DC voltage, such as several thousand volts, e.g. 15 kilovolts (kV), on the center discharge electrode causes a corona discharge to develop near the electrode due to high electric field intensity. This creates charge carriers that cause ionization of the gas in the gap between the high voltage electrode and the ground collector electrode. As the gas containing suspended particles flows through this region, the particles are electrically charged by the ions. The charged particles are then precipitated electrostatically by the electric field onto the interior surface of the collecting tube or canister.
Electrostatic precipitators have been used in diesel engine crankcase ventilation systems for removing suspended particulate matter including oil droplets from the blowby gas, for example so that the blowby gas can be returned to the atmosphere, or to the fresh air intake side of the diesel engine for further combustion, thus providing a blowby gas recirculation system. Electrostatic precipitators are also used in other internal combustion engine electrostatic crankcase ventilation systems for receiving recirculation gas from the engine, and returning cleaned gas to the engine. Electrostatic precipitators are also used in other applications, e.g. oil mist recirculation in a compressor, and various other applications for collecting particulate ionized in an electric field created by a high voltage corona discharge electrode.
A corona discharge electrode assembly commonly used in the prior art has a holder or bobbin with a 0.006 inch diameter wire strung in a diagonal direction. The bobbin is provided by a central drum extending along an axis and having a pair of annular flanges axially spaced along the drum and extending radially outwardly therefrom. The wire is a continuous member strung back and forth between the annular flanges to provide a plurality of segments supported by and extending between the annular flanges and strung axially and partially spirally diagonally between the flanges.
When an electrostatic precipitator is in service on a diesel engine, a build-up of sludge often occurs on the grounded electrode, i.e. the annular ground plane provided by the canister. This sludge build-up can cause a degradation of the performance of the precipitator, and increases frequency of arcing. The rate of build-up is exacerbated by the arcing, and in turn the arcing increases with the build-up of such material. Eventually, the efficiency of the precipitator decreases due to high frequency (e.g. 400 Hz or greater) arcing and other unstable events which can last for a duration on the order of a minute. In addition to causing a decrease in efficiency, the arcing causes stress on electrical components including the power supply due to the discharge/charge process of arcing. This is problematic in automotive applications which require long service life, or at least extended intervals between servicing, which has limited the application of this technology.
One solution to the noted problem is to periodically clean the collector electrode to remove the build-up therefrom, e.g. by impact or vibration which may be mechanically induced, e.g. mechanical rapping, or by acoustical vibration. This is not satisfactory in the case of crankcase blowby because the particles are liquid, and the build-up is sticky, particularly in the presence of arcing.
Another solution known in the prior art is to clean the electrode by a mechanical wiper automatically during operation. This is undesirable because it requires mechanical parts subject to failure, and increases cost by adding components.
The noted parent '541 application provides a solution wherein the electrostatic precipitator or droplet collector is provided with a replaceable electrode assembly which is connectable and removable in a simple servicing step enabling and facilitating replacement at regular service intervals. In preferred form, part of the precipitator is permanent and remains attached to the engine or an underhood mounting location, and only low cost items are replaced. The ease of servicing promotes periodic replacement, thus avoiding the noted degradation of performance. In further preferred form, the electrode assembly is replaced in a simple spin-on, spin-off step, comparable to replacing an oil filter. This familiarity is considered desirable to encourage maintenance at recommended intervals by service personnel, without having to learn unfamiliar service procedures. In one embodiment, both the collector electrode and the corona discharge electrode are removed as a unit from a mounting head in the system. In another embodiment, only the collector electrode is removed.
The present invention provides a further solution, and enables extended service intervals, improved electrostatic precipitator performance, extended service life of the power supply, and reduced energy usage.